Investigating the wind-sand flow response regularity in the longitudinal slope sections of desert highways provides a scientific basis for selecting the slope of desert roads.This study uses the Tengger Desert section...Investigating the wind-sand flow response regularity in the longitudinal slope sections of desert highways provides a scientific basis for selecting the slope of desert roads.This study uses the Tengger Desert section of the Wuhai-Maqin Expressway as a case study,employing CFD numerical simulation methods to calculate and analyze the wind-sand flow field distribution characteristics in different longitudinal slope sections.The results show that:(1)Along with the direction of the incoming flow,the windward and leeward slope toes of the embankment are low-wind-speed zones,with the wind speed at the leeward slope toe being even lower.The higher the embankment,the larger the low-wind-speed zone at the windward and leeward slope toes.As the longitudinal slope increases,the extent of the lowwind-speed zone at the same location along the route also increases.(2)Along the route direction,the wind speed at the windward and leeward slope toes decreases as embankment height increases.At the embankment toe,sand particles are transported from the top to the bottom of the longitudinal slope,and the greater the longitudinal slope,the stronger the transport effect.(3)Along the route direction,the sand accumulation around the embankment gradually gathers toward the bottom of the longitudinal slope as the slope increases.When the longitudinal slope is 3%and 4%,the trend of sand accumulation moving from the windward side at the end of the route to the leeward side at the start of the route is more significant.When the longitudinal slope is less than or equal to 3%,severe sand accumulation within the embankment range is reduced by 86.4%or more compared to when the slope is 4%.(4)Under the same longitudinal slope,the higher the embankment height,the smaller its transport rate.When the embankment height is the same,the greater the longitudinal slope,the greater the embankment transport rate.展开更多
Using seasonally collected data(2009-2010) from 15 sampling sites that represent first- to fifth-order streams within the Qingyi watershed,we examined the spatio-temporal patterns of fish assemblages along two longitu...Using seasonally collected data(2009-2010) from 15 sampling sites that represent first- to fifth-order streams within the Qingyi watershed,we examined the spatio-temporal patterns of fish assemblages along two longitudinal gradients to explore the effects of a large dam on fish assemblages at the watershed scale.No significant variation was observed in either species richness or assemblage structure across seasons.Species richness significantly varied according to stream order and gradient.Dam construction appeared to decrease species richness upstream substantially,while a significant decrease between gradients only occurred within fourth-order streams.Along the gradient without the large dam,fish assemblage structures presented distinct separation between two neighboring stream orders,with the exception of fourth-order versus fifth-order streams.However,the gradient disrupted by a large dam displayed the opposite pattern in the spatial variation of fish assemblages related with stream orders.Significant between-gradient differences in fish assemblage structures were only observed within fourth-order streams.Species distributions were determined by local habitat environmental factors,including elevation,substrate,water depth,current discharge,wetted width,and conductivity.Our results suggested that dam construction might alter the longitudinal pattern in fish species richness and assemblage structure in Qingyi Stream,despite the localized nature of the ecological effect of dams.展开更多
This paper describes the drift-diffusion theory of the bipolar field-effect transistor （BiFET） with two identical and connected metal-oxide-silicon-gates （MOS-gates） on a thin-pure-base. Analytical solution is obt...This paper describes the drift-diffusion theory of the bipolar field-effect transistor （BiFET） with two identical and connected metal-oxide-silicon-gates （MOS-gates） on a thin-pure-base. Analytical solution is obtained by partitioning the two-dimensional transistor into two one-dimensional problems coupled by the parametric sur- face-electric-potential. Total and component output and transfer currents and conductances versus D. C. voltages from the drift-diffusion theory, and their deviations from the electrochemical （quasi-Fermi） potential-gradient theory,are presented over practical ranges of thicknesses of the silicon base and gate oxide. A substantial contri- bution from the longitudinal gradient of the square of the transverse electric field is shown.展开更多
基金financially supported by Youth Science“Research on Failure Mechanism and Evaluation Method of Sand Control Measures for Railway Machinery in Sandy Area”(12302511)Ningxia Transportation Department Science and Technology Project(20200173)The Central Guidance on Local Science and Technology Development Funds(22ZY1QA005)。
文摘Investigating the wind-sand flow response regularity in the longitudinal slope sections of desert highways provides a scientific basis for selecting the slope of desert roads.This study uses the Tengger Desert section of the Wuhai-Maqin Expressway as a case study,employing CFD numerical simulation methods to calculate and analyze the wind-sand flow field distribution characteristics in different longitudinal slope sections.The results show that:(1)Along with the direction of the incoming flow,the windward and leeward slope toes of the embankment are low-wind-speed zones,with the wind speed at the leeward slope toe being even lower.The higher the embankment,the larger the low-wind-speed zone at the windward and leeward slope toes.As the longitudinal slope increases,the extent of the lowwind-speed zone at the same location along the route also increases.(2)Along the route direction,the wind speed at the windward and leeward slope toes decreases as embankment height increases.At the embankment toe,sand particles are transported from the top to the bottom of the longitudinal slope,and the greater the longitudinal slope,the stronger the transport effect.(3)Along the route direction,the sand accumulation around the embankment gradually gathers toward the bottom of the longitudinal slope as the slope increases.When the longitudinal slope is 3%and 4%,the trend of sand accumulation moving from the windward side at the end of the route to the leeward side at the start of the route is more significant.When the longitudinal slope is less than or equal to 3%,severe sand accumulation within the embankment range is reduced by 86.4%or more compared to when the slope is 4%.(4)Under the same longitudinal slope,the higher the embankment height,the smaller its transport rate.When the embankment height is the same,the greater the longitudinal slope,the greater the embankment transport rate.
基金Foundation items： This study was financially supported by the National Basic Research Program of China （2009CB119200） and the Natural Science Foundation of China （31071900, 31172120）
文摘Using seasonally collected data(2009-2010) from 15 sampling sites that represent first- to fifth-order streams within the Qingyi watershed,we examined the spatio-temporal patterns of fish assemblages along two longitudinal gradients to explore the effects of a large dam on fish assemblages at the watershed scale.No significant variation was observed in either species richness or assemblage structure across seasons.Species richness significantly varied according to stream order and gradient.Dam construction appeared to decrease species richness upstream substantially,while a significant decrease between gradients only occurred within fourth-order streams.Along the gradient without the large dam,fish assemblage structures presented distinct separation between two neighboring stream orders,with the exception of fourth-order versus fifth-order streams.However,the gradient disrupted by a large dam displayed the opposite pattern in the spatial variation of fish assemblages related with stream orders.Significant between-gradient differences in fish assemblage structures were only observed within fourth-order streams.Species distributions were determined by local habitat environmental factors,including elevation,substrate,water depth,current discharge,wetted width,and conductivity.Our results suggested that dam construction might alter the longitudinal pattern in fish species richness and assemblage structure in Qingyi Stream,despite the localized nature of the ecological effect of dams.
文摘This paper describes the drift-diffusion theory of the bipolar field-effect transistor （BiFET） with two identical and connected metal-oxide-silicon-gates （MOS-gates） on a thin-pure-base. Analytical solution is obtained by partitioning the two-dimensional transistor into two one-dimensional problems coupled by the parametric sur- face-electric-potential. Total and component output and transfer currents and conductances versus D. C. voltages from the drift-diffusion theory, and their deviations from the electrochemical （quasi-Fermi） potential-gradient theory,are presented over practical ranges of thicknesses of the silicon base and gate oxide. A substantial contri- bution from the longitudinal gradient of the square of the transverse electric field is shown.
